1. Field of the Invention
The present invention relates to an exposure calculating apparatus for a camera.
In order to expose a photographing medium such as a film under a proper exposure condition in a camera, a diaphragm equipped in a taking lens and an exposure time need be controlled in correspondence with the light amount of an object and therearound, and this control processing is performed by an exposure calculating apparatus equipped in the camera.
The present invention also relates to a camera having a visual axis detecting device and, more particularly, to a camera having a visual axis detecting device for performing focusing control and exposure control using a position of visual axis obtained from the direction of an eyeball of a photographer as a position of object in a field.
The present invention further relates to an object perceiving apparatus for detecting a position occupied by an object seen by a photographer in a field caught by a taking lens equipped in a camera.
2. Related Background Art
As a conventional exposure control method, a method of determining an exposure value according to the light amount from the central portion of a field under an assumption that an object is present at the central portion of the field of a taking lens is known.
In this case, an exposure calculating apparatus is constituted using, as a photometric or light-metering element for measuring the light amount of the field, a photometric element having characteristics in which the sensitivity of a portion corresponding to the central portion of the field is maximal, and the sensitivity is monotonously decreased toward the surrounding portion of the field. An exposure value is determined according to an output from the photometric element.
Such an arrangement is called a center-weighted photometric system. When this system is adopted, the arrangement of the exposure calculating apparatus can be simplified.
In the case of the above-mentioned center-weighted photometric system, however, when the brightness value of the central portion is considerably different from that of the surrounding portion like in a photographing operation in a strong back-light state, a proper exposure value cannot often be obtained.
In order to solve this problem, a method of dividing the field into a plurality of photometric areas, as shown in FIG. 1, and determining an exposure value in consideration of balance of the light amounts of the respective photometric areas is also known. This method is called a divisional photometric method.
In this case, the exposure calculating apparatus is constituted by arranging photometric elements corresponding to the photometric areas, and the brightness values of the photometric areas are obtained based on the photometric results obtained by independently measuring the photometric areas. The exposure value is determined based on these brightness values.
Since the divisional photometric method is executed under an assumption that the object is present at the central portion of the field, when the exposure value is to be calculated, the photometric result from the central circular photometric area of the five photometric areas shown in FIG. 1 is weighted with a large value.
Since the above-mentioned conventional methods are executed under an assumption that the object is present at the central portion, when a photographing operation is performed while catching the object at the surrounding portion of the field, a proper exposure value cannot often be obtained depending on the above-mentioned exposure calculating apparatuses.
As a method of obtaining a proper exposure value in such a case, a technique for selecting a photometric pattern corresponding to a position of object from some photometric patterns, and obtaining an exposure value conforming to the object is disclosed in Japanese Laid-Open Patent Application No. 2-32312 entitled "Visual Axis Input Camera".
FIG. 2 is a schematic diagram showing the arrangement of an exposure calculating apparatus of the above-mentioned visual axis input camera.
In FIG. 2, the exposure calculating apparatus comprises a focusing lens 1, photometric elements 2 divided as a plurality of areas, and a microprocessor 3 for performing exposure calculating processing on the basis of photometric results from the photometric elements 2. An image formed on a focusing screen 5 provided on a prospective focal plane of a taking lens 4 is formed on the photometric elements 2 through a pentagonal prism 6 by the above-mentioned focusing lens 1.
The photometric elements 2 are divided, as shown in FIG. 3, and photometric operations can be independently performed in units of areas. The microprocessor 3 changes weights to be given to the photometric results of the above-mentioned areas to obtain photometric results corresponding to a case wherein the position of the maximal value of the photometric sensitivity distribution of the photometric elements 2 is varied, thereby calculating an exposure value.
A visual axis detecting circuit 7 observes the eyeball of a photographer through an eyepiece lens 8 to discriminate the direction of visual axis of the photographer, thereby obtaining a position of visual axis where the visual axis of the photographer crosses the field. This position of visual axis is input to the microprocessor 3 as a position of object.
Therefore, when the microprocessor 3 changes the weights to be given to the photometric results of the areas according to the input position of object, the photometric result equivalent to that obtained when the photometric operation of the field is performed using a photometric element which has the photometric sensitivity distribution having the maximal sensitivity at the position of object, can be obtained.
In this manner, exposure control can be performed to have the position of object as the central position of the center-weighted photometric method, and exposure control conforming to the object in correspondence with the brightness of the object present at the surrounding portion of the field can be performed.
This technique, however, can only vary the central position of the photometric sensitivity distribution in the center-weighted photometric system. Therefore, since the balance of the entire field is not taken into consideration, a portion surrounding the object may be overexposed in a back-light photographing operation, and a portion darker than the object may not be photographed at all.
In a conventional camera, focusing control and exposure control are performed on the basis of information of the central portion of the field under an assumption that the object is present at the central portion of the field of a taking lens equipped in the camera.
A photographing operation is often performed to have a composition in which the object is offset from the center. A demand has arisen for focusing control and exposure control on the basis of information of an object portion located at a position offset from the central portion in correspondence with the above-mentioned case.
In order to meet this demand, the following technique is proposed. That is, the direction of visual axis of a photographer is obtained based on the direction of the eyeball of the photographer by utilizing the fact that the photographer gazes at the object, and focusing control and exposure control are performed using a position of visual axis where the visual axis crosses the field as an object position.
As a technique for detecting the position of visual axis of a photographer as an object position, and performing focusing control and exposure control based on the position of visual axis, a technique disclosed in Japanese Laid-Open Patent Application No. 63-94232 entitled "Camera Controlling Apparatus" is known.
FIG. 4 shows the arrangement of the above-mentioned camera controlling apparatus.
In FIG. 4, a photographing circuit 9 comprises a two-dimensional CCD element (to be simply referred to as a CCD hereinafter) 10, and an image is formed on the CCD 10 by a photographing optical system consisting of a taking lens 4 and a diaphragm 11.
In FIG. 4, a movement of eyeball detecting device 12 discriminates the direction of the eyeball from the position of a pupil, and sends the discrimination result to a gate controlling circuit 13 (see Journal of the Institute of Television Engineers of Japan, Vol. 40, No. 2, 1986, pp. 121-128.
The gate controlling circuit 13 generates a gate controlling signal for controlling to open/close a gate 15 on the basis of the discrimination result and horizontal and vertical sync signals from a clock circuit 14, and instructs to open the gate 15 according to an output from the CCD 10 corresponding to the gazing portion of the photographer indicated by the above-mentioned discrimination result. Then, the gazing portion of the photographer is extracted from an output from the photographing circuit 9, and is supplied to an automatic focusing (AF) controlling circuit 16, and an automatic exposure (AE) controlling circuit 17. Thus, the extracted information is subjected to control processing of a lens driving device 18 and a diaphragm driving device 19.
In this manner, there is provided the camera controlling apparatus, which can perform focusing control and exposure control on the basis of information of the position of visual axis of a photographer who looks at an object through the finder, and can perform camera control on the basis of information of the object portion regardless of the position of the object in the field.
In the conventional method, the position of visual axis of the photographer obtained from the direction of the eyeball is used as the object position. However, the photographer does not always gaze at an object, but gazes at an area other than the object to check the balance of the composition or gazes at information associated with exposure control displayed outside the frame. For this reason, when the position of visual axis is used as the object position, an object intended by the photographer cannot often be correctly perceived.
In particular, when the photographer blinks or gazes at information displayed outside the frame, the movement of eyeball detecting device 12 cannot discriminate the object position, and focusing control and exposure control may be disabled.
Since the eyeball always moves, and the position of visual axis changes from time to time according to this movement, the exposure value and the focus position vary according to the position of visual axis which changes from time to time, resulting in unstable exposure control and focusing control. In particular, the eyeball often moves abruptly. In this case, the above-mentioned instability of the control becomes conspicuous.